Radio device and measuring device utilizing electrostatic microrelay and electrostatic microrelay

ABSTRACT

A protrusion  24  that is formed on at least any one of a fixed substrate  10  and a moveable substrate  20  contacts the remained another substrate  20  or  10  after a moveable substrate  20  is operated and before the contacts are closed.

BACKGROUND OF THE INVENTION

[0001] Conventionally, there has been provided an electrostaticmicrorelay shown in FIG. 11A and FIG. 11B (Japanese Patent Laid-OpenPublication HEI5-2976).

[0002] In this electrostatic microrelay, a moveable substrate 202 iselastically supported in a frame-like support portion 201 provided onthe surface of a fixed substrate 200 so that a fixed electrode 203formed on the upper surface of the fixed substrate 200 and a moveableelectrode 204 formed on the lower surface of the moveable substrate 202are placed opposite to each other. By applying voltage between theelectrode 203 and the electrode 204, electrostatic attraction force isgenerated to attract the moveable electrode 204 toward the fixedelectrode 203. As a result, the moveable substrate 202 is bent such thatthe moveable terminal 205 contacts the fixed terminal 206 to close therelay.

[0003] However, in the electrostatic microrelay, when the relay isclosed at the terminals, cohesion or adhesion may occur. Therefore, inorder to reliably break the contact of the terminals, elastic recoveryforce needs to be increased. For this reason, it becomes necessary toincrease electrostatic attraction force between the electrodes, by, forexample, increasing driving voltage (voltage applied between theelectrodes), increasing the electrode area where the electrodes arefacing to each other; decreasing the distance between the electrodes, orusing an electret. As a result, the volume of the microrelay has beenincreased and electric voltage durability of the terminals has beendeteriorated, and structure and machining process of the microrelaybecame more complicated, resulting in increase of production cost.

SUMMARY OF THE INVENTION

[0004] Therefore, it is an object of the present invention to provide amicrorelay having a excellent capability of breaking the contact of theterminals under a simple and small structure and which can be easilymanufactured at low-cost as well as a radio device and a measuringdevice utilizing the electrostatic microrelay.

[0005] In order to achieve the above object, the present inventionprovides an electrostatic microrelay which comprises a fixed substratehaving a fixed electrode thereon, and a moveable substrate having amoveable electrode thereon, the moveable substrate positioned a selecteddistance from the fixed substrate, the moveable substrate facing thefixed substrate supported by a support member, wherein application ofvoltage between the moveable substrate and the fixed substrate generatesan electrostatic attraction force therebetween so as to move themoveable electrode toward the fixed substrate so that a moveableterminal formed on the moveable substrate contacts a fixed terminalformed on the fixed substrate to close the microrelay. The electrostaticmicrorelay comprises a protrusion provided on at least one of the fixedsubstrate and the moveable substrate wherein the protrusion provided onone of the substrates contacts the other substrate after the movement ofthe moveable substrate toward the fixed substrate but before theterminals are closed.

[0006] Under this configuration, when a voltage is applied between theelectrodes to generate electrostatic attraction force therebetween, aportion of the moveable substrate extending from the support memberthereof is elastically deformed and a protrusion provided on either oneof the substrates contacts the other substrate. By this movement, themoveable electrode comes close to the fixed electrode, therebyincreasing the electrostatic attraction force. As a result, the moveablesubstrate is partially elastically deformed around the protrusion, andthe moveable electrode is adhered to the fixed electrode such that themoveable terminals are closed at the fixed terminals. Thereafter, if thevoltage applied between the electrodes is removed, the electrostaticattraction force disappears. In addition, the elastic force generated bythe bent of the extending portion and the elastic force caused by thepartial deformation of the protrusion at the time of contact with thesubstrate works as the separation force of the terminals. And once theprotrusion is separated from the substrate, the moveable substrate isrecovered to its original opposing position portion due to the elasticforce generated by the bent of the whole body.

[0007] The protrusion may be formed at least at one position between thesupport member and the moveable terminal.

[0008] The height of the protrusion may be the height or less at whichthe terminals can be closed by elastically deforming the moveablesubstrate at nearby the protrusion by using the electrostatic attractionforce generated between the electrodes. For example, the height of theprotrusion may be determined to be one third of the distance between theseparated substrates. Under this configuration, the closing of theterminals is not obstructed by the existence of the protrusion which isprovided to increase the separation force of the terminal.

[0009] By evenly supporting the moveable substrate via a plurality ofbeam members which extends from the moveable substrate, the moveableelectrode may be smoothly moved both before and after the protrusioncontacts the substrate.

[0010] The beam members elastically support the moveable substrate attwo positions in point symmetry around the moveable terminal,

[0011] the signal lines are positioned on a single straight line on afixed substrate,

[0012] the portion of the moveable substrate which opposes the signalline is removed, the moveable terminals are elastically supported at twopositions which perpendicularly crosses the straight line of the signalline but does not face the signal lines,

[0013] a pair of protrusions may be point-symmetrically formed aroundthe moveable terminals where the protrusion first contacts either one ofthe substrate after the close of the terminal.

[0014] Under this configuration, the terminal breaking force can bechanged in two stages corresponding to the change of electrostaticattraction force, regardless of the configuration which is adapted tothe open-close operation of high frequency signals. Namely, in the rangewhere the electrostatic attraction force is weak, the protrusions do notcontact the opposing substrate, and the moveable substrate is easilydeformed in accordance with electrostatic attraction force. Also, in therange where electrostatic attraction force is strong, the elastic forceof the moveable substrate becomes large owing to the contact of theprotrusions to the opposing substrate. Moreover, the protrusion isformed in the position where it first contacts the opposing substrateafter the terminals are closed. Therefore, because the elastic force ofthe moveable substrate can be changed at the most suitable position inrelation to the electrostatic attraction curve, it becomes possible toimprove the terminal separation characteristics.

[0015] The protrusions may be formed on any one of the substrates in theportions that the substrate contacts the opposing substrate after theprotrusion contacts the opposing substrate in order of precedence inwhich since change of the electric force by the side of the moveablecontact can be made to meet the electrostatic attraction curve, it isenable to obtain suitable force of contact-breaking.

[0016] The protrusion may be formed of insulation material. By removingelectrode from the portion where the protrusions contact, the adhesionof organic materials between the protrusion and the electrode can beprevented, thereby achieving desired stable performance characteristicsfor a long period of time.

[0017] In addition, the electrostatic microrelay having the aboveconfiguration is suitable for opening and closing terminals used inwireless transmission apparatus and/or high frequency signal devices,such as radio device and measuring devices.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1A is a plane view of an electrostatic microrelay accordingto an embodiment of the present invention and

[0019]FIG. 1B is a sectional view of FIG. 1.

[0020]FIG. 2 is a disassembled perspective view of the electrostaticmicrorelay of FIG. 1.

[0021] FIGS. 3A-3I are sectional views showing manufacturing process ofFIG. 1.

[0022]FIG. 4A-FIG. 4D are schematic view showing performing state of theelectrostatic microrelay of FIG. 1.

[0023]FIG. 5 is a graph showing the relationship between a distance ofthe electrodes and electrostatic attraction force.

[0024]FIG. 6A is a plane view of an electrostatic microleray accordingto another embodiment of the present invention and

[0025]FIG. 6B is a sectional view of FIG. 6A.

[0026]FIG. 7 is a disassembled perspective view of the electrostaticmicrorelay according to another embodiment of the present invention.

[0027]FIG. 8 is a perspective view showing the state of the moveablesubstrate of FIG. 7 from another angle.

[0028]FIG. 9 is a block diagram showing the state of using theelectrostatic microrelay of FIG. 1 in a wireless device.

[0029]FIG. 10 is a block diagram showing the state of using theelectrostatic microrelay of FIG. 1 in a measuring device.

[0030]FIG. 11A and FIG. 11B are partial front view of the electrostaticmicrorelay according to a conventional example and a front view showingthe state of one-side hitting at the time of in operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring now to the accompanying drawings, embodiments; of thepresent invention are explained as follows.

[0032]FIG. 1 and FIG. 2 show an electrostatic microrelay according to anembodiment of the present invention. The electrostatic microrelayincludes a fixed substrate 10 made of a glass substrate 11 a and amoveable substrate 20 provided on a top surface of the fixed substrate10.

[0033] The fixed substrate 10 includes a fixed electrode 12 and fixedterminals 13, 14 both formed on the top surface of the glass substrate11 a. The outer surface of the fixed electrode 12 is coated with aninsulating film 15. The fixed electrode 12 and the fixed terminals 13,14 are connected to connecting pads 16 and 17, 18 via printed connectionpaths 16 a and 17 a, 18 a respectively.

[0034] The moveable substrate 20 includes a moveable electrode 25 evenlysupported by four of the first beam members 22, each extending sidewardfrom top surface ends of the support members 21 which is provided at thetop surface of the fixed substrate 10. Protrusions 24 are formed at thebottom surface where the first beam member 22 and the moveable electrode25 are connected each other. When the moveable substrate 20 is bent dueto the electrostatic attraction force, the protrusions 24 contacts thefixed substrate 10 before the terminals are closed. Also, theprotrusions 24 are formed such that when the protrusions 24 contacts thefixed substrate 10 the distance between the electrodes 12 and 25 becomesless than one third of the distance between the fixed substrate 10 andthe moveable substrate 20. Under this configuration, becauseelectrostatic attraction force becomes dramatically increased at thetime when the protrusions 24 contact the fixed substrate 10, it becomespossible to reliably have the moveable electrode 25 attracted to thefixed substrate 12 regardless of the existence of the protrusions 24.

[0035] In addition, although the above protrusions 24 are formed con themoveable substrate 20, it may be formed on the fixed substrate 10 or onboth substrates 10, 20. Also, the protrusions 24 may be formed at morethan two positions between the terminals 13, 14, 28 and the supportmember 21.

[0036] The support member 21 is connected to the connecting pad 19 via aprinted connection path 19 a which is provided on the top surface of thefixed substrate 10. At the center of the moveable electrode 25, a secondbeam member 23 is formed by a pair of slits 26 b, 26 c. At the center ofthe bottom surface of the second beam member 23, a moveable terminal 28is formed by using an insulation film 27. The moveable terminal 28 facesthe fixed terminals 13, 14 in a manner that they can be separated orclosed.

[0037] Next, the process for producing an electrostatic microrelayhaving the above configuration is explained.

[0038] First, as shown in FIG. 3B, the fixed electrode 12 and the fixedterminals 13, 14 are formed on the glass substrate 11 a made of amaterial, such as Pyrex, as shown in FIG. 3A. Also, printed connectionpaths 16 a, 17 a, 18 a, and 19 a and the connecting pads 16, 17, 18 and19 are formed thereon respectively. Thereafter, by coating the fixedelectrode 12 with an insulating film 15, the base 10 is completed asshown in FIG. 3C.

[0039] In addition, by using a silicon oxide having a relativedielectric constant of 3-6 or a silicon nitride having a relativedielectric constant of 7-8 as the insulating film 15, largeelectrostatic attraction force can be obtained and therefore contactload can be increased.

[0040] On the other hand, as shown in FIG. 3D, in order to form aterminal gap at the bottom surface of an SOI wafer 100, which isconsisted of a silicon layer 101, a silicon oxide layer 102 and asilicon layer 103 in this order from the top, wet etching processing isperformed by TMAH having silicon oxide film as a mask, and form asupport member 21 and a protrusion 24 both protruding downward areformed as shown in FIG. 3E. Then, as shown in FIG. 3F, the moveableterminal 28 is formed after coating with an insulating film 27.

[0041] Next, as shown in FIG. 3G, the SOI wafer 100 is integrallyattached to the base 10 by anodic bonding. Then, as shown in FIG. 3H,the SOI wafer 100 is thinned by etching the top surface thereof by usingalkali etchant such as TMAH or KOH so that the silicon oxide layer 102is exposed outside. Further, the silicon oxide layer 102 is removed byusing fluoric etchant, making the silicon layer 103, which becomes themoveable electrode 25, exposed outside, as shown in FIG. 3I. Thereafter,pattern-drawing etching is conducted by dry etching processing usingRIFE or the like to form a cutout 26 a and slits 26 b, 26 c, therebyforming the first and second beam members thereon. By this processing,production of the moveable substrate 20 is completed.

[0042] The base 10 can be produced not only from the glass substrate 11a but also from a single crystal silicon substrate having at least aninsulating film coated thereon.

[0043] Next, performance of the electrostatic microrelay having theabove configuration is explained with reference to a schematic drawingof FIG. 4.

[0044] When no voltage is applied between the electrodes as shown inFIG. 4A, the first beam member 11 is not elastically deformed andmaintains the state where the first beam member 11 is horizontallyextending. In this state, the moveable substrate 20 faces the fixedsubstrate 1 in a predetermined distance. Therefore, the moveableterminal 16 is separated from the fixed terminals 7 a, 7 b.

[0045] Under this condition, if a voltage is applied between theelectrodes to generate a electrostatic attraction force therebetween,the first beam member 11 is elastically deformed such that the moveablesubstrate 2 comes closer to the fixed substrate 1. As a result, as shownin FIG. 4B, the protrusions 17 contact the fixed substrate 1. As shownin FIG. 5, the electrostatic attraction force increases as the distancebetween the electrodes becomes small. If the protrusions 17 eventuallycontact the fixed substrate 1, the electrostatic attraction forcebetween the electrodes 4 and 12 dramatically increases. Therefore, thesurrounding portions of the protrusions 17 are partially elasticallydeformed and the moveable electrode 12 becomes adhered to the fixedelectrode 4. (consequently, as shown in FIG. 4C, the moveable terminal16 contacts the terminal 7 to close the terminal. After the moveableterminal 16 has contacted the fixed terminal 7, the second beam member13 becomes bent in addition to the first beam portions 22 as shown inFIG. 4D and the moveable electrode 12 is attracted to the fixedelectrode 4. Therefore, as the surrounding moveable electrode 12 isadhered to the fixed electrode 4, the moveable terminal 16 is pressed tothe fixed terminal 4 via the second beam member 13. Therefore,occurrence of one-side hitting is prevented and the contact reliabilityis improved.

[0046] In this case, if the force to pull the moveable electrode 12upward caused by the first and second beam 11 and 13 are respectivelyexpressed as F_(s1) and F_(s2), the force to pull the moveable electrode12 upward caused by the elastic deformation of the surrounding portionof the protrusion 17 which occurs when the protrusion 17 contacts thefixed substrate 1 to close the terminal is expressed as F_(s3), theelectrostatic attraction force generated between the moveable electrode12 and the fixed electrode 4 being interposed by the insulating film 6is expressed as F_(e), and the resisting force derived from the surfaceof the insulating film 6 is expressed as F_(n), the followingrelationship exists:

F _(e) =F _(s1) +F _(s2) +F _(s3) +F _(n)

[0047] By adjusting the spring constant, the initial gap between themoveable electrode 12, the fixed electrode 4, and the thickness of theterminals, the values of F_(n) and F_(s1) can be made small and,therefore, decrease of the value of F_(s2), namely decrease of thecontacting force (from the idealistic model), can be prevented.

[0048] Thereafter, by removing the voltage applied between theelectrodes, not only the elastic force of the first and second beammembers 11 and 13 but also the elastic force caused by the deformationof the surrounding portion of the protrusions 17 works as the force toseparate the terminals. For this reason, the terminals can be reliablyseparated even if the terminals are adhered or cohered to each other.After the contact of the terminals is separated, the moveable substrate2 is restored to its original position by the elastic force of the firstbeam member 11 after the terminals are separated and until theprotrusions 24 are separated from the fixed substrate 10.

[0049] As explained above, in the above embodiment, due to the formationof the protrusions 17, it becomes possible to largely increase the forceto break the terminal and have the moveable substrate 2 move smoothlywhen the applied voltage is removed.

[0050] Also, because the whole body of the moveable substrate 2 is madeof a silicon wafer alone and point-symmetrically formed between left andright and line-symmetrically formed in cross section, deflection and/ortorsion of the moveable electrode is prevented. As a result,inoperability and uncertainty of operation performance characteristicscan be effectively avoided and smooth operation characteristics can beensured.

[0051] Also, because the whole body of the moveable substrate 2 is madeof a silicon wafer alone and point-symmetrically formed between left andright and line-symmetrically formed in cross section, deflection and/ortorsion of the moveable electrode is prevented. As a result,inoperability and uncertainty of operation performance characteristicscan be effectively prevented and smooth operation characteristics can beensured.

[0052] Also, the configuration of the electrostatic microrelay may bethe one shown in FIG. 6 that is similar to the conventionalconfiguration which is shown in FIG. 9.

[0053] Namely, this electrostatic microrelay is formed of a rectangularframe body wherein a support member 31 is provided on the top surface ofa fixed substrate 30. A moveable substrate 40 is cantilevered by aconnecting member 32 at an interior edge of the support member 31. Aninsulation film 41 is provided on the bottom surface of the moveablesubstrate 40 and a moveable contact 42 is formed on the free side endthereof. Also, a protrusion 43 is formed between the moveable terminal42 and the connecting member 32. The protrusion 43 contacts the fixedsubstrate 30 before the moveable terminal 42 is closed at the fixedterminal 33.

[0054] In addition, according to the above embodiment, although themoveable electrodes 25, 40 are formed in a flat shape, they may beformed in a thin shape having a concavity formed on top surface thereof.Under this configuration, the operation speed and recovery speed can befurther improved while maintaining desired strength and light weight.

[0055] The moveable electrodes 25, 40 may be made larger in thicknessthan the beam portions 22, 23 so that the strength of the electrodesbecomes larger. Under this configuration, the electrostatic attractionforce can be fully transformed into the attraction force for themoveable electrodes 12, 40, so that the electrostatic attraction forcecan be efficiently used to deform the first beam member 22 and/or theconnecting member 32.

[0056] The embodiment may be formed like the one shown in FIG. 7.

[0057] Namely, signal lines 55 a and 55 b are positioned on a samestraight line. Terminals 57 a and 57 b are provided next to each otherin a predetermined distance in the central area of the a glass substrate53. The fixed electrode 54 is provided with a connection pad 58 d forapplying a voltage and a connection pad 58 e for grounding. Theconnection pad 58 e works to prevent leakage of signal when highfrequency signal is transmitted by using the signal lines 55 a, 55 b.

[0058] The moveable substrate 52 shown in FIG. 8 has a configurationthat the moveable electrode 62 is evenly supported by the two first beammembers 61 which extends sideward from the support member 60 standing onthe top surface of the fixed substrate 51. In the center of the moveableelectrode 62, there is provided a terminal block 64 which is supportedby a pair of the second beams 63. The portion which faces the signalline is removed. At the bottom surface of the moveable electrode 62,there are provided the protrusions 67 formed at the point-symmetricalposition around the moveable terminal 66. More specifically, theprotrusions 67 are formed at the positions where the moveable electrode62 first contacts the fixed electrode 4. According to thisconfiguration, when the moveable substrate 52 is bent due to theelectrostatic attraction force, the protrusions 67 contact the fixedsubstrate 51 before the terminals are closed. Under this condition, theincrease of the breaking force and decrease of the contacting forcecaused by the increase becomes idealistic rate condition.

[0059] The protrusion 67 is closer to the opposing fixed substrate 54than the other portion (of the moveable electrode 62). Thus, theelectrostatic attraction force becomes large so that electric fieldbecomes concentrated. And, if a foreign matter, such as an organicmaterial, exists around the protrusion, such foreign matter is attractedto the protrusion 67 where electric field is concentrated and iseventually adhered to the protrusion. In this case, it is possible thatthe height of the protrusion 67 is changed and the operationcharacteristics become unstable. Therefore, as shown in FIG. 7, there isprovided a non-electric portion 68 which does not have the fixedelectrode 54 in the position facing the protrusion 67. However, if theprotrusions 67 are made of insulating material, such as an oxide film,the generation of the electrostatic force can be decreased. In thiscase, the non-electric portion 68 is not necessary. Also, if theprotrusion 67 is formed, for example, in a half pillar shape,concentration of electric field can be decreased and therefore foreignmatters are not attracted. As shown in FIG. 4D, for example, during wetetching by TMAH with silicon oxide used as a mask is performed, theprotrusions 67 may be formed together with the support potions 60. Theprotrusions 67 may be formed on the fixed substrate 1 or on bothsubstrates. Further, more than two pairs of the protrusions 67 may beformed between the terminals and the support member 60. In this case,protrusion 67 can be formed at the position where the moveable substrate2 contacts the fixed substrate 1 after the protrusion 67 contacts thefixed substrate 51. (in FIG. 7, in order of a, b and c shown by thedotted line). Under this configuration, it becomes possible to stabilizethe contacting force and breaking force.

[0060] Although, in the above embodiment, the moveable substrate issupported by four or two first beam members 22 or 61, the moveablesubstrate may be supported by three, five, or more beam members. Underthis configuration, the area efficiency of the electrostatic microrelaycan be enhanced.

[0061] Because the above described electrostatic microrelay MR has thecharacteristic of effectively transmitting direct-current and highfrequency signals in a good condition with low loss, it can be used in aradio device 110 shown in FIG. 9 or a measuring device 120 shown in FIG.10. In FIG. 9, the electrostatic microrelay MR is connected between aninternal circuit 112 and an antenna 113. In FIG. 10, the electrostaticmicrorelay MR is connected in the middle of each signal line from aninternal circuit 121 to a measurement subject (not shown). By using themicrorelay of the present invention, signals can be transmitted withhigh accuracy and less burden to an amplifier used in the internalcircuit as compared to a conventional element. Also, because themicrorelay of the present invention is small in size and consumes lesselectricity, it can fulfill its performance especially in a batterydriven wireless device or measuring device.

What is claimed is:
 1. An electrostatic microrelay comprising a fixedsubstrate having a fixed electrode thereon, and a moveable substratehaving a moveable electrode thereon, the moveable substrate positioned apredetermined distance from the fixed substrate, the moveable substratefacing the fixed substrate supported by a support member, whereinapplication of voltage between the moveable electrode and the fixedelectrode generates an electrostatic attraction force therebetween so asto move the moveable substrate so that a moveable terminal formed on themoveable substrate contacts a fixed terminal formed on the fixedsubstrate to close the microrelay, the electrostatic microrelay furthercomprising; a protrusion provided on at least one of the fixed substrateand the moveable substrate; wherein the protrusion provided on one ofthe substrates contacts the other substrate after the movement of themoveable substrate prior to the contact of the terminals.
 2. Theelectrostatic microrelay according to claim 1, wherein the protrusion isformed at least at one position between the support member and theterminals.
 3. The electrostatic microrelay according to claim 1, whereinheight of the protrusion is equal to or less than a height under whichthe moveable substrate can be elastically deformed to close the terminalnearby the protrusion due to the electrostatic attraction force at atime the protrusion contacts the other substrate.
 4. The electrostaticmicrorelay according to claim 1, wherein the moveable substrate isevenly supported by a plurality of beam members which e extend from thesupport member, and the protrusion is evenly provided corresponding toeach beam member.
 5. The electrostatic microrelay according to claim 4,wherein the beam member elastically support the moveable substrate attwo point-symmetrical positions around the moveable terminal, the signallines are aligned on the fixed substrate as each fixed contact of oneend of the signal line is next to each other with a given distance, themoveable substrate is removed at least the portion opposed to the signalline and supports the moveable contact at the two position which isrectangular to the signal line and is not opposed to the signal line, apair of protrusions are so formed as to be point-symmetrical focussingon the moveable contact in any one of the substrates in the portion thatcontacts the opposing substrate after coming into contact.
 6. Theelectrostatic microrelay according to claim 5, wherein the protrusionsare formed on any one of the substrates in the portions that thesubstrate contacts the opposing substrate after the protrusion contactsthe opposing substrate in order of precedence.
 7. The electrostaticmicrorelay according to claim 1, wherein the protrusion is formed ofinsulating material.
 8. The electrostatic microrelay according to claim1, wherein electrode is removed at a position where the protrusioncontacts the substrate.
 9. A wireless device wherein an electrostaticmicrorelay according to claim 1 or 5 is provided such that electricalsignals are opened or closed between an antenna and an internal circuit.10. A measuring device wherein an electrostatic microrelay according toclaim 1 or 5 is provided such that electrical signals are opened orclosed between a measuring object and an internal circuit.